1. Field of the Invention
The present invention relates to a forced air-cooled magnetron apparatus suitable for use in microwave ovens and the like.
2. Description of the Prior Art
In general, magnetron apparatus of the forced air-cooled type, used in microwave ovens or similar devices, has a magnetron anode cylinder which is provided on the outer peripheral surface thereof with a multiplicity of heat radiating fins arranged in a plurality of stages, and cooling air is forced to flow through the gaps between adjacent heat radiating fins. The cooling air effectively cools the magnetron so as to suppress any tendency of temperature rise in the magnetron, thereby preventing unfavorable effects such as operation failure due to abnormal temperature rise or reduction in the coercive force of a permanent magnet due to temperature rise.
However, attaching a multiplicity of heat radiating fins to the outer peripheral surface of the magnetron anode cylinder requires troublesome work which makes it difficult to mass-produce the magnetron.
FIG. 1 exemplarily shows a typical known method for attaching the heat-radiating fins to the outer peripheral surface of the anode cylinder 1. According to this method, heat-radiating fins 2, 4 are successively attached to the outer peripheral surface of the magnetron anode cylinder 1 by, for example, pressfitting, such that cylindrical portion 5 of each horizontal fin fits around the cylindrical surface of the anode cylinder 1. This attaching method involves a risk in that the cylindrical portion 5 of the heat-radiating fin 4 is superposed to the cylindrically-deformed portion 3 of the preceding heat-radiating fin 2. This not only causes an irregularity in the gaps between adjacent heat-radiating fin but makes it impossible to obtain a large area of contact between the cylindrically-deformed portion 5 and the anode cylinder 1, thus impairing the heat-radiation effect significantly.
Another problem is that the anode cylinder 1, which is heated to a high temperature, cannot be effectively cooled by the air, because the flow E of the cooling air passing through the gap between adjacent heat-radiating fin 2, 4 is largely deflected to both lateral sides in the region near the magnetron anode cylinder 1 as shown in FIG. 2.